t.i.i.I.registerProducer(producer, streaming) : method documentation

This sets self to be a consumer for a producer. When this object runs
out of data (as when a send(2) call on a socket succeeds in moving the last
data from a userspace buffer into a kernelspace buffer), it will ask the
producer to resumeProducing().

For IPullProducer
providers, resumeProducing will be called once each time data
is required.

For IPushProducer
providers, pauseProducing will be called whenever the write
buffer fills up and resumeProducing will only be called when
it empties.